1. Field of the Invention
The present invention relates to an apparatus for vaporizing and supplying a material which is used for supplying a gas to a chemical vapor deposition (CVD) apparatus or a physical vapor deposition (PVD) apparatus used for production of semiconductors. More specifically, the present invention relates to an apparatus which vaporizes and supplies a liquid CVD material for production of semiconductors which is unstable at higher temperatures highly accurately at a desired flow rate without causing deterioration in the quality.
2. Description of the Related Arts
Forming films such as semiconductor films, insulation films and metal films is necessary in the production of semiconductor devices. The major processes for forming films are the physical vapor deposition (PVD) in which vacuum vapor deposition or sputtering is used and the chemical vapor deposition (CVD) in which light energy or heat energy is used. CVD is mainly used because of easier control. In accordance with this process, a material for the treatment is placed in an atmosphere of a CVD gas such as an organometallic compound which is supplied from an apparatus for supplying a gas. The CVD gas is decomposed by supplying light energy or heat energy to the material for the treatment, and a film such as a semiconductor film, insulation film or a metal film is formed on the surface of the material for the treatment.
Films having more improved properties are required as semiconductor devices having higher degrees of integration and showing higher speeds are supplied with more variety. Organosilicon compounds and organoaluminum compounds have heretofore been used as the CVD material for forming the above films. Under the above circumstances, other organic compounds such as organotantalum compounds, organobarium compounds, organotitanium compounds, organotungsten compounds, organocopper compounds, organostrontium compounds and organozirconium compounds are also being examined as the CVD material for forming the above films.
When any of the above CVD material is used, it is necessary that the supplied gas in the production of semiconductors have a high purity and that the concentration of the gas and the amount of the supply be accurately controlled. Many of the above materials have low vapor pressures and high viscosities and are unstable at high temperatures. Therefore, it is also necessary that a CVD material be vaporized and supplied to a CVD apparatus without deterioration in the quality.
Various methods for vaporizing a CVD material and supplying the material to a CVD apparatus in a vapor phase have been known. Examples of such methods include (1) a method in which a carrier gas is blown into a heated liquid material to vaporize the material, (2) a method in which a liquid material at an ordinary or raised temperature is evacuated to form the vapor of the material, (3) a method in which a liquid material is sprayed to a heated vaporizer under a pressure to form the vapor of the material (Japanese Patent Application Laid-Open No. Heisei 6(1994)-310444), (4) a method in which a carrier gas is introduced into the vapor phase portion of a liquid material in a heated vessel to decrease the concentration of the material in the vapor phase and the vapor of the material is supplemented from the liquid phase, and (5) a method in which a liquid material is atomized by an ultrasonic vibrator disposed at a lower part of a vessel of the liquid material and then introduced into a heated vaporizer to form the vapor of the material (Japanese Patent Application Laid-Open No. Heisei 7(1995)-278817).
However, the above methods have the following problems. In the method (1), the concentration of the gas obtained by the vaporization is different depending on the amount of the supplied carrier gas and the efficiency of contact between the liquid material and the carrier gas, and a portion of the material becomes a mist rather than the vapor. In the method (2), the condition of the operation of a CVD apparatus is limited to a reduced pressure. In the method (3), the amount supplied to a CVD apparatus cannot be set to a desired value because the condition of the material obtained by the atomization is different to a great extent depending on the pressure and the flow rate in the spraying under a pressure. In the method (4), the liquid material is decomposed and deteriorated while being heated in the vessel. In the method (5), the control of the concentration of the vaporized gas is difficult because the liquid material is supplied in the atomized condition, and a filter or a collision plate must be disposed in the vaporizer to prevent supplying a mist of the material to a CVD apparatus.